Diagnosis: Similar to R. altivelisZBK , R. atratusZBK , R. ornatusZBK , R. rectocaudatusZBK , R. romeriZBK , R. tecminaeZBK , and R. uaktiZBK , and distinguished from all other congeners by possessing a frontal squamation pattern consisting of one scale with all margins exposed just posterior to snout (vs. scale with all margins exposed near the center of median portion of frontal region) and an oblique infraorbital dark gray bar through chin (vs. never a similar color pattern). Similar to R. tecminaeZBK and R. rectocaudatusZBK and distinguished from all other species of the genus by the caudal fin truncate in males (vs. rounded or subtruncate). Distinguished from R. tecminaeZBK and R. rectocaudatusZBK by having more scales on the longitudinal series (48-49, vs. 38-43), flank with oblique rows of bright green dots in females (vs. bright green dots absent), caudal fin with dark red line on the dorsal and ventral margins in males (vs. dark marginal line absent). Differs from R. tecminaeZBK by having short pelvic fins, their tips reaching the anterior portion of the anal-fin base in males (vs. reaching the middle of anal-fin base). Differs from R. rectocaudatusZBK by having flank with narrow red stripes in males (vs. horizontal rows of orange spots) and hyaline caudal fin in females (vs. pale yellow with bright yellow stripe on dorsal and ventral margins).

Description: Morphometric data given in Table 2. Male larger than female, largest male 39.9 mm SL. Dorsal profile slightly convex from snout to end of dorsal-fin base, approximately straight on caudal peduncle. Ventral profile convex on head, almost straight from anterior portion of venter to end of anal-fin base, nearly straight on caudal peduncle. Body slender, subcylindrical anteriorly, slightly deeper than wide, to compressed posteriorly. Greatest body depth at level of pelvic-fin base.

Habitat notes: All specimens of the type series were collected in small shallow temporary pools within the forest, about 0.5-2.0 m of diameter, and about -15 cm deep (Fig. 6). The water was turbid and the bottom was litter. No other fish was found in these pools, which were almost contiguous to a lagoon, where no specimen of the new species was found.

Etymology: The name amana-pira-miri (amana = rain, pira = fish, miri = small) was recorded by Wallace as the Indian native name for a smaller species similar to R. amanapiraZBK , collected by him in the upper rio Negro region, tentatively now identified as R. tecminaeZBK . This note was recently published (Wallace, 2002) in a book consisting of fish drawings and respective notes made during Wallace’s journey to Amazon (1850-1852). According to the notes, the fish is found in small pools in the litter within the forest after rain (exactly the same conditions in which R. amanapiraZBK was collected), and consequently the Indians believed that it failed with the rain from the sky. Wallace (2002) mentions another Indian name for the species, owiyeye, which was also mentioned by a Tucano Indian at the moment of the collection of the type series of R. amanapiraZBK .

Discussion

Monophyly of the R. atratus species groupZBK (i. e., R. atratusZBK , R. ornatusZBK , R. rectocaudatusZBK , R. romeriZBK , R. uaktiZBK , R. tecminaeZBK , and R. amanapiraZBK ) is tentatively supported by two apomorphic features: frontal squamation consisting of one scale with all margins exposed just posterior to snout (Huber, 1992; Costa, 2003c) and an oblique infraorbital dark gray bar through chin (Costa, 2003c). In all other species of RivulusZBK and in other rivulids, all the scales of the anterior portion of the frontal region have the posterior margin overlapped by the anterior margin of the scale posterior to them, the scales with all margins free are uniquely placed near the center of the frontal region; and, there is never an infraorbital oblique bar ventrally extending to cross the chin.

Among species of the R. atratus groupZBK , Rivulus uaktiZBK , R. romeriZBK , R. tecminaeZBK , and R. amanapiraZBK share two apomorphic conditions: preopercular canal and dermosphenotic absent. Rivulus rectocaudatusZBK , not examined in the present study, probably is a member of this group, since it shares some derived conditions with Rivulus uaktiZBK , R. tecminaeZBK , and R. amanapiraZBK (presence of caudal spot in males; see below), and with R. tecminaeZBK and R. amanapiraZBK (caudal fin truncate in males). The preopercular canal is present in all other species of RivulusZBK , except in species of the R. punctatus groupZBK (Costa, 1995a, 1998) that includes R. apiamici CostaZBK , R. decoratus CostaZBK , R. modestus CostaZBK , R. paracatuensis CostaZBK , R. pictus CostaZBK , R. pinima CostaZBK , R. punctatus BoulengerZBK , R. violaceus CostaZBK , and R. zygonectes MyersZBK ; the dermosphenotic is present in all other species of RivulusZBK . Absence of dermosphenotic both in the R. punctatus species groupZBK , and in an assemblage within the R. atratus groupZBK is possibly homoplastic, since the R. punctatus species groupZBK is closely related to species with a preopercular canal (Costa, 1995a, 1998), none of them possessing the diagnostic derived features of the R. atratus species groupZBK .

A group comprised of R. uaktiZBK , R. tecminaeZBK , R. rectocaudatusZBK and R. amanapiraZBK , is supported by the presence of a pale spot on the caudal-fin base of males. In other species, a spot on the caudal-fin base is present only in juveniles and adult females. However, two derived features occurring in these four species have an incongruent distribution. Whereas, a truncate caudal fin in males is uniquely shared by R. amanapiraZBK , R. rectocaudatusZBK , and R. tecminaeZBK , a long pelvic fin is uniquely shared by R. uaktiZBK and R. tecminaeZBK . Rivulus altivelisZBK , not examined in the present study, shares with R. uaktiZBK and R. tecminaeZBK the possession of long pelvic fins, but has a different frontal squamation pattern (Huber, 1992), making doubtful its phylogenetic relationships without examination of osteological features.